The present invention relates to an improvement for tube heaters including radiant tube heaters.
Tube heaters are devices utilized to transfer heat from burners to a material while also isolating the atmosphere about the materials from the products of combustion of the burners. The tube heaters themselves can be uni-directional or bi-directional. Uni-directional heaters have a single, continuously firing burner at one end of the tube and an exhaust at the other. Bi-directional heaters have an alternately, selectively operating burner with air preheating, regenerative heat-exchange matrix and exhaust at both ends of the tube. Either type of tube heater is functional. However, in both types of devices a difficulty is experienced in controlling the combustion intensity along the length of the tube. This creates a maldistribution of temperature along such length. This maldistribution of temperature can cause shortened life of the tube, undesirable heat flux distribution into the process, and less effective use of the entire tube surface area. While the bi-directional, regenerative arrangement is better than the uni-directional, the gross BTU of either input must be limited for a specific tube diameter. This is particularly troublesome for tubes with large length/diameter ratios. Heat recovery devices that reclaim waste heat by preheating combustion further exacerbate the aforementioned problem due to higher flame temperatures. In addition to the temperature distribution problems of tube heaters, nitrogen oxide generation is also increased by higher flame temperature.
These problems limit the market for tube heaters.